1. Field of the Invention
The present invention relates to an efficient energy delivery system which can be employed with any number of large scale transport vessels to deliver fluid to a semiconductor, light emitting diode or liquid crystal display manufacturer. In particular, the energy delivery system is removable from the transport vessel, yet maintains the integrity necessary to deliver energy to the vessel in an efficient manner.
2. Description of Related Art
Industrial processing and manufacturing applications such as semiconductor, light emitting diode (LED), liquid crystal display (LCD) manufacture require processing steps which employ one or more non-air fluids. It will be understood by those skilled in the art that “non-air” fluids or gases refer to fluids (in various phases) which are not derived from the constituent components of air. As utilized herein, non-air fluids or gases include, but are not limited to, ammonia, boron trichloride, carbon dioxide, chlorine, dichlorosilane, halocarbons, etc. Specifically, the manufacture requires the application of non-air gases in vapor phase.
Generally, gases are delivered to the manufacturer's facility in a transport vessel, which is utilized as part of the delivery mechanism. Fluid is removed from this vessel in vapor phase and delivered to the point-of-use in a discontinuous manner.
The ultimate application requires that the vapor phase gas contain a relatively low level of low volatility contaminants, as otherwise these contaminants can deposit on the product substrate (e.g., semiconductor wafer, LCD motherglass or LED sapphire base). Deposition of these low volatility contaminants, which include water, metal and particulates, can produce a number of deleterious effects, including reduced brightness (LED manufacture) and yield loss (semiconductor, LCD, or LED manufacture).
Fluids such as silane and nitrogen trifluoride are delivered and stored in vapor phase. Since low volatility components do not evaporate readily, their concentration in these fluids is typically low. Other non-air fluids or gases are transported and stored as liquids or vapor/liquid mixtures. These gases are commonly known as low vapor pressure gases, and include, for example, ammonia, hydrogen chloride, carbon dioxide, and dichlorosilane. These fluids typically have a vapor pressure of less than 1,500 psig at a temperature of 70° F. A complex mechanism is necessary to deliver these latter gases to the point-of-use in vapor phase at the requisite purity, since the conversion of stored liquid low vapor pressure gases into vapor tends to cause the low volatility contaminants to vaporize.
Some systems convert stored liquid low vapor pressure gases into vapor by withdrawing liquid from the transport vessel and partially vaporizing same in a separate vessel. These systems generate a contaminant-enriched liquid waste which must be transferred for disposal. Further, they require a mechanism for transferring liquid from the transport vessel to the vaporization vessel, necessitating a pump or an inert gas pressurization mechanism.
Other systems are designed to vaporize liquid phase low vapor pressure gas in the transport vessel. In small scale systems, this vaporization means may be readily transferred from one vessel to another as the liquid content is exhausted. However, in larger supply systems, such as ISO container based systems, it is difficult to transfer the vaporization means from one transport vessel to another because the heaters and their attachment mechanism are cumbersome. Further, these heaters often do not conform well to large vessels, resulting in poor heat transfer, high heat losses, heater burn out and the formation of “hot spots” on the transport vessel. “Hot spots” are a potential safety issue, since transport vessels are typically not designed for high temperature.
Another significant drawback to these systems is that they can cause vigorous liquid phase low vapor pressure gas boiling. Such boiling can cause liquid droplets containing low volatility contaminants to be entrained and carried into the vapor phase.
In light of the numerous issues associated with the production and delivery of vapor phase low vapor pressure fluid from either a liquid or two-phase non-air fluid, a number of proposals for low vapor pressure fluid vaporization have been made in the related art.
One such proposal has been provided in U.S. Pat. Nos. 4,833,299 and 5,197,595. The apparatus described in these patents consist of flexible heaters, insulation, a fabric such as a flexible heater/insulation unit, and a releasable means for securing opposite ends of the housing unit to the vessel. The apparatus described by these documents, however, are small vertical cylinders, where the heaters wrap around the entire vessel circumference.
U.S. Pat. No. 6,025,576 discloses a heated transport vessel for low vapor pressure gases withdrawn therefrom. The heaters are in tensioned contact with the transport vessel. One of the disadvantages with such a system is that heaters could sag, bulge or otherwise wrinkle and lose the contact with the vessel wall. As a result, the energy transfer to the vessel is not uniform or efficient.
U.S. Pat. No. 6,614,009 relates to a supply of ultra high purity gases in large volumes and high flow rates from a container of liquefied gas. The heaters are permanently positioned onto the container. Therefore devices simply cannot be removed and attached to another vessel.
U.S. Pat. No. 6,363,728 discusses a system for controlled delivery of a gas from a liquefied state where the heat exchangers are in contact with the transport vessel. The heat exchangers are either of the type where the liquid transfer media is circulated through a metallic coil or alternatively an electric heater embedded in a metallic coil. However, these systems do not evenly distribute energy, nor do they conform to the contour of the vessel.
U.S. Pat. No. 6,581,412 likewise discusses a system for controlled delivery of a gas from a liquefied state where the heat exchangers are in contact with the transport vessel. The heat exchangers described are heating jackets and hot water or oil baths. Oil baths are impractical for large scale systems. As described in this patent, heating jackets are designed for higher temperature to compensate for a poor contact between the heaters and the vessel. Moreover, the frequent changes of the compressed gas vessel, which is inevitable at high flow rates, reduces the contact effectiveness.
Some of the disadvantages related to the systems of the latter described documents are that they result in poor energy transfer and premature heater and vessel failure. Specifically, the heating devices are not readily usable on various transport/storage vessels, and lack the requisite efficiency to deliver the vapor phase fluid at a high flow rate while maintaining the purity required at the point-of-use.
To overcome the disadvantages of the related art, it is an object of the present invention to provide an uncomplicated system for the delivery of a vapor phase non-air gas from a liquefied compressed gas cylinder to a point-of-use.
It is another object of the invention, to provide a system for delivering vapor phase fluid at an elevated pressure from the transport/storage vessel, where the energy delivery devices are configured and held in contact with the vessel wall so as to efficiently deliver energy to the vessel. In particular, the heating means are held in close contact with the wall of the transport/storage vessel, and substantially eliminates the uneven distribution of energy.
It is yet another object of the invention, to provide an energy delivery system that is adapted to be removed and utilized on various transport/storage vessels. Moreover, the energy delivery devices of this system can readily be removed and replaced in the event of failure.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.